Perhaps I should not mention my own work here, but in the book "Rock
garden design and construction," which I edited for Timber
Press/NARGS, there is a chapter on bulb and alpine frames, with good
line drawings by Suky McDonough (our correspondent Mark's wife), and
photos of the extensive bulb frames where I used to grow my
collection. In the photo book "Bulbs" by Martyn Rix and Roger
Phillips, there is a photo in the introduction of a bulb frame under
construction; it is apparently designed to grow the bulbs in the fill
soil, not in pots.
To the descriptions already posted, I would add that it is strongly
advisable to include some kind of barrier at the bottom of the frame.
I use industrial-strength woven groundcloth, which for many years has
deterred moles from digging in from below -- and where moles pioneer
a tunnel, mice and voles are sure to follow. I used this same product
to line the raised beds where my bulbs are now growing, as well as
the path between the beds, which is paved with crushed rock. The beds
are under a polycarb roof in a commercial steel-frame greenhouse with
metal mesh walls.
Although most cold frames are of the "shed" design, with hinges on
one side, I think it's far better to have an "A-frame" design that
opens on both sides for access and ventilation. However, building an
A-frame takes more carpentry skills than I have (i.e., more than
none), so I paid someone else to build mine. In the UK gardeners can
buy "Access" frames that are made like miniature greenhouses with
opening panels on the sides, but I've heard anecdotally that these
don't stand up well to heavy snow loads or strong winds.
Jane McGary
Portland, Oregon, USA